Cochlear implants have become extremely successful at restoring hearing in deaf individuals. Although they work well in quiet environments, almost all users have great difficulty understanding speech in the presence of noise. Bilateral cochlear implants are provided to a growing number of patients in an effort to alleviate this problem because binaural hearing in normal-hearing listeners is known to greatly enhance the ability to segregate speech from background noise. However, the benefits in bilateral cochlear implants users reported to date are modest compared with what is seen in normal-hearing persons. An obvious problem is that present cochlear implants processing schemes do not provide the information required to allow two devices to work together optimally. The proposed work will test the hypothesis that a key mechanism for enhancing speech discrimination by bilateral cochlear implant users is binaural unmasking via interaural correlation sensitivity. Although binaural unmasking cues have been well-studied in acoustic hearing, they remain poorly understood with cochlear implants. The proposed research builds on our novel preliminary finding that bilateral cochlear implant users can exploit interaural differences to improve signal detection in noise. The proposed research will investigate binaural signal detection and speech discrimination using two complementary paradigms. We will test (1) bilateral cochlear implant users and (2) normal-hearing subjects listening to stimuli chosen to be analogous to those used in the implant experiments. The proposed work will expand our knowledge of the binaural system using the novel stimuli available with cochlear implants and will allow the development of sound processors to produce better speech understanding in noise by cochlear implant users. Our research will also help inform an important question in the clinical world: whether cochlear implant users should get one or two devices. Knowing the magnitude of the bilateral cochlear implant advantages and how to maximize those advantages will inform this clinical debate. Bilateral cochlear implants are provided to a growing number of patients in an effort to improve speech understanding in the presence of noise because binaural hearing in normal-hearing listeners is known to provide such improvements. However, the benefits in bilateral cochlear implant users reported to date are modest compared with what is seen in normal-hearing persons. By studying how fundamental binaural cues are perceived by bilateral cochlear implant users we aim to develop processors to maximize the benefits bilateral cochlear implant users can obtain from their devices.